I also have had accounts with both and closed out my IB account because I hadn't used it in a few months due to the difference in commissions i was paying (much more with IB, though it's $5 per 1000 shares, not $50 as you said). Plus IB's customer service and other tools are pretty poor in my opinion. However, I don't daytrade, I take positions for about a week on average. I did think they were great for trading options.

tentenequals20, Are you saying that you can use StrategyDesk generated orders for the same Ameritrade account in which you pay $5/trade commissions? Does that same Ameritrade account in which you pay $5/trade commissions also let you have Level-II, GainsKeeper, etc. for free?

Their "Command Center" allows you to select an ECN or MMID to direct an order to. I've often directed orders to ISLD/Inet and used the reserve order/hidden size function. Most likely market orders are shopped around, but on the limit side, they do offer direct access options.

How did you get $5 commission charge with TD? I've had a TD Apex account for about 5 years now but I am still being charged $9.99. Did you call and and ask comparing other brokers for the deal? Or is this discount for account activity?

yes, discount for account activity
and correct get all services like level 2 etc., for free as well.

Def, thanks for clarity on modify/cancel.
sounds like all other points of comparison are accurate. I shd add the no interest upto 10K as a downside to IB as well.
but fills could be better, which is unknown to me.